And I'm Robert Siegel. Oklahoma has released new details about the botched execution this week of convicted murderer Clayton Lockett. It took 43 minutes for Lockett to die, and his death came from a heart attack after the execution was halted. In a moment, we'll hear about how lethal injection became the standard method of execution in the U.S. First, here's NPR's Greg Allen with the latest on Oklahoma's investigation into what went wrong.

GREG ALLEN, BYLINE: The new details show Clayton Lockett's execution was more trouble than first reported. In a timeline release by the head of Oklahoma's Department of Corrections, the problems began early Tuesday morning, when Lockett resisted being taken from his cell. Prison guards used a Taser to subdue him. When they took him to an examination room, they learned he had slashed his right arm. It was determined stitches weren't necessary.

But the most serious problems began around 5:30 Tuesday evening, when Lockett was taken into the execution chamber. For more than 50 minutes, a medical technician looked, without success, for a vein into which a catheter could be inserted. Finally, an IV needle was inserted into a vein in Lockett's groin area.

During the execution, after he was declared unconscious, Lockett writhed and tried to lift his head. After more than a half-hour, the doctor found his vein had collapsed. Prison authorities called off the execution. Ten minutes later, however, Oklahoma authorities say Lockett died of a heart attack. Madelyn Cohen is an assistant federal public defender who represents Charles Warner, the next person on Oklahoma's death row scheduled for execution. She says the problems with Lockett's execution raise a host of questions.

MADELYN COHEN: What was happening to Mr. Lockett? Was he being administered a proper IV? Were the drugs going into his system what they purported to be? Was anybody involved in the process trained to do this procedure?

ALLEN: Oklahoma's governor, Mary Fallin, has ordered a review of what went wrong in the execution. She said this week it would be conducted by a member of her Cabinet.

GOV. MARY FALLIN: I expect the review process to be deliberate, to be thorough. And it will be the first step in evaluating our state's execution protocols.

ALLEN: Yesterday Fallin's corrections chief, Robert Patton, said he believed the review should be conducted by an independent, outside agency. In other recommendations, Patton said the state should adopt what he called proven standards in conducting executions. He said that staff should be given extensive training in whatever new protocols are developed. And Patton recommended an indefinite stay for Charles Warner, currently set for a May 13th execution date. Warner's lawyer, Madelyn Cohen, welcomes all of these recommendations.

COHEN: We need to do some legal work to ensure that the indefinite stay recommended by Director Patton is implemented by the courts, and that this May 13th date is not hanging over Mr. Warner's head while we sort all of these problems out.

ALLEN: In Washington today, President Obama said he was asking Attorney General Eric Holder to look into events surrounding the botched execution in Oklahoma. What happened in Oklahoma, he said, is deeply troubling. Obama said the case showed there are, quote, "significant questions about how the death penalty is being applied."

While public support for the death penalty has been dropping in recent years, a majority tell pollsters they're still in favor of it. Despite the problems with Lockett's execution this week, Oklahoma's governor, Mary Fallin, said she believes justice sometimes requires the death penalty.

FALLIN: I believe the legal process worked. I believe the death penalty is an appropriate response and punishment to those who commit heinous crimes against their fellow men and women.

ALLEN: Lockett was convicted of beating and raping a 19-year-old woman, Stephanie Neiman. She was then buried alive. Defense attorneys who represent inmates on death row say in many states, corrections departments have become increasingly secretive about how executions are conducted, and what drugs are used. In the aftermath of the botched Oklahoma execution, several say they hope the courts will begin to lift the veil on the secrecy surrounding executions.